Single cell photovoltaic module

ABSTRACT

A photovoltaic module includes a first transparent electrode layer characterized by a first sheet resistance, a second transparent electrode layer, and a photovoltaic material layer. The photovoltaic material layer is located between the first transparent electrode layer and the second transparent electrode layer. The photovoltaic module also includes a first busbar having a second sheet resistance lower than the first sheet resistance. The first transparent electrode layer, the second transparent electrode layer, and the photovoltaic material layer have an aligned region that forms a central transparent area of the photovoltaic module. The central transparent area including a plurality of sides. The first busbar is in contact with the first transparent electrode layer adjacent to at least a portion of each of the plurality of sides of the central transparent area.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 62/423,581, filed Nov. 17, 2016, entitled “SINGLE CELL PHOTOVOLTAICMODULE,” the disclosure of which is hereby incorporated by reference inits entirety for all purposes.

FIELD OF THE INVENTION

This invention relates to the field of photovoltaic modules and devicesand more particularly, single cell photovoltaic modules.

BACKGROUND OF THE INVENTION

Photovoltaic (PV) cells with partial light transmission have beendeveloped to provide electrical power for a variety of applications,including windows, mobile devices, and information displays. However,there is a need in the art for improved methods and systems related toPV modules.

SUMMARY OF THE INVENTION

Embodiment described herein relate to photovoltaic modules with lowpower loss caused by series resistance. A single cell transparentphotovoltaic module with minimized visible patterns and minimized powerloss from series resistance is disclosed. The photovoltaic module caninclude a first and second transparent electrode that each have acontinuous central area and a periphery with a photovoltaic materialpositioned between the first and second transparent electrodes. Eachtransparent electrode can be contacted by a low-resistance electricalbusbar in contact with each side of the periphery to minimize thedistance of current travel. In some embodiments current travel isminimized by making electrical contact to interdigitated contact pointson the top and bottom electrode adjacent to the periphery. Thetransparent photovoltaic module can be integrated into variousapplications such as being overlaid onto an information display toprovide electrical power to the device.

In some embodiments, a single cell photovoltaic module may include atransparent bottom electrode layer, an active layer, and a transparenttop electrode layer. In certain embodiments, a top busbar having a sheetresistance lower than the sheet resistance of the top electrode layermay be in contact with the full or near full periphery of the topelectrode layer to reduce the series resistance associated with the topelectrode layer. Additionally or alternatively, a bottom busbar having asheet resistance lower than the sheet resistance of the bottom electrodelayer may be in contact with the full or near full periphery of thebottom electrode layer to reduce the series resistance associated withthe bottom electrode layer. In some embodiments, the top electrode layer(or the top busbar) may be connected to a first set of contact pads, thebottom electrode layer (or the bottom busbar) may include or beconnected to a second set of contact pads, and the first set of contactpads may be arranged interdigitatedly with respect to the second set ofcontact pads. In some embodiments, a cell of the photovoltaic module mayinclude multiple junctions connected in series to increase the outputvoltage while limiting the output current of the cell, such that powerloss caused by the series resistance may be limited as well. In variousimplementations, these and other techniques disclosed herein may be usedindividually or in combination.

According to an embodiment of the present invention, a photovoltaicmodule is provided. The photovoltaic module includes a first transparentelectrode layer characterized by a first sheet resistance, a secondtransparent electrode layer, and a photovoltaic material layer. Thephotovoltaic material layer is located between the first transparentelectrode layer and the second transparent electrode layer. Thephotovoltaic module also includes a first busbar having a second sheetresistance lower than the first sheet resistance. The first transparentelectrode layer, the second transparent electrode layer, and thephotovoltaic material layer have an aligned region that forms a centraltransparent area of the photovoltaic module. The central transparentarea includes a plurality of sides. The first busbar is in contact withthe first transparent electrode layer adjacent at least a portion ofeach of the plurality of sides of the central transparent area. Inanother embodiment, the first busbar is in contact (e.g., electricalcontact) with the first transparent electrode layer adjacent at least aportion of each of two or more of the plurality of sides of the centraltransparent area.

In an embodiment, the first busbar is in contact with the firsttransparent electrode layer at a plurality of contact locations on eachof the plurality of sides of the central transparent area. In anotherembodiment, the photovoltaic module also includes a contact pad locatedproximal to the second transparent electrode layer. The first busbar iselectrically coupled to the contact pad. In yet another embodiment, thephotovoltaic module additionally includes a plurality of contact padslocated proximal to the second transparent electrode layer. The firstbusbar is electrically coupled to one or more of the plurality ofcontact pads. In yet another embodiment, the photovoltaic moduleincludes a first set of contact pads located proximal to the secondtransparent electrode layer, the first set of contact pads coupled tothe first busbar and a second set of contact pads located proximal tothe second transparent electrode layer. The second set of contact padsare coupled to the second busbar and the first set of contact pads isarranged interdigitatedly relative to the second set of contact pads.

According to another embodiment of the present invention, a photovoltaicmodule is provided. The photovoltaic module includes a first transparentelectrode layer including a contiguous first central region and a firstset of electrode pads electrically coupled to the contiguous firstcentral region. The photovoltaic module also includes a secondtransparent electrode layer including a contiguous second central regionand a second set of electrode pads electrically coupled to thecontiguous second central region. The photovoltaic module furtherincludes a photovoltaic material layer located between the firsttransparent electrode layer and the second transparent electrode layer.The contiguous first central region, the contiguous second centralregion, and the photovoltaic material layer are aligned to form acentral transparent area of the photovoltaic module, the centraltransparent area including a plurality of sides. At least one of thefirst set of electrode pads and at least one of the second set ofelectrode pads are positioned on each of the plurality of sides of thecentral transparent area.

According to a specific embodiment of the present invention, aphotovoltaic module is provided. The photovoltaic module includes afirst transparent electrode layer including a contiguous first centralregion and a first set of electrode pads electrically coupled to thecontiguous first central region. The photovoltaic module also includes asecond transparent electrode layer including a contiguous second centralregion and a second set of electrode pads electrically coupled to thecontiguous second central region. The photovoltaic module furtherincludes a photovoltaic material layer located between the firsttransparent electrode layer and the second transparent electrode layer.The contiguous first central region, the contiguous second centralregion, and the photovoltaic material layer are aligned to form acentral transparent area of the photovoltaic module, the centraltransparent area having a perimeter that includes a plurality ofsegments. At least one of the first set of electrode pads and at leastone of the second set of electrode pads are positioned on each segmentof the plurality of segments of the perimeter of the central transparentarea.

Numerous benefits are achieved by way of the present invention overconventional techniques. For example, embodiments of the presentinvention provide single cell transparent photovoltaic modules withreduced visible patterns and reduced power loss from series resistance.In some embodiments current travel is reduced in comparison withconventional designs by making electrical contact to interdigitatedcontact points on the top and bottom electrode adjacent to theperiphery. These and other embodiments of the invention along with manyof its advantages and features are described in more detail inconjunction with the text below and attached figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a schematic of an active area of a photovoltaic cellaccording to an embodiment of the present invention;

FIG. 1B shows the effect of active area sheet resistance on resistivepower loss;

FIG. 2A shows a monolithic series integrated solar cell with 8 sub-cellsin series;

FIG. 2B shows an expanded plan view of a portion of the monolithicseries integrated solar cell illustrated in FIG. 2A;

FIG. 2C is a cross-sectional view of the monolithic series integratedsolar cell at line 2C in FIG. 2A.

FIG. 3A is a plan view of a single cell photovoltaic module according toan embodiment of the present invention;

FIG. 3B is a plan view of a series integrated photovoltaic module;

FIGS. 4A-D show the direction of charge travel in a single cell modulewith an increasing number of contacts;

FIG. 5 shows a table with dimensionless ratios of charge traveldistances for different perimeter contact configurations;

FIG. 6A is a cross-sectional view of an example single cell modulehaving two contacts according to an embodiment of the present invention;

FIG. 6B is a plan view of an example single cell module having twocontacts according to an embodiment of the present invention;

FIG. 7 shows dimensionless ratios of charge travel distances fordifferent two-contact configurations of a single cell module;

FIG. 8A is a cross-sectional view of an example single cell module withinterdigitated contact pads according to an embodiment of the presentinvention;

FIG. 8B is a plan view of an example single cell module withinterdigitated contact pads according to an embodiment of the presentinvention;

FIGS. 8C-8N show a breakout of each layer of a single cell moduleaccording to an embodiment of the present invention;

FIG. 8P shows an exploded view of the single cell module according to anembodiment of the present invention;

FIG. 9 shows dimensionless ratios of charge travel distances fordifferent interdigitated contact configurations;

FIG. 10 shows dimensionless ratios of charge travel distance as afunction of the number of contacts per edge for an active area;

FIG. 11A shows a plan view of a photovoltaic cell with an interdigitatedcontact arrangement according to an embodiment of the present invention;

FIG. 11B shows an exploded view of a photovoltaic cell with aninterdigitated contact arrangement according to an embodiment of thepresent invention;

FIGS. 12A-12B show photovoltaic cells according to various geometricarrangements according to an embodiment of the present invention;

FIG. 13 shows a photovoltaic cell according to a circular arrangementaccording to an embodiment of the present invention;

FIG. 14 shows a perspective view of various methods of contacting asingle cell module according to an embodiment of the present invention;

FIG. 15A is a cross-sectional view of a single cell module with aperimeter busbar for one or more electrodes according to an embodimentof the present invention;

FIG. 15B is a perspective view of a single cell module with perimeterbusbar for one or more electrodes according to an embodiment of thepresent invention;

FIG. 16A is a plan view of a single cell module with busbars in contactwith the perimeter of an electrode according to an embodiment of thepresent invention;

FIG. 16B is a first cross-sectional view of a single cell module withbusbars in contact with the perimeter of an electrode according to anembodiment of the present invention;

FIG. 16C is a second cross-sectional view of a single cell module withbusbars in contact with the perimeter of an electrode according to anembodiment of the present invention;

FIGS. 17A-F show a breakout of each layer of a single cell module withbusbars in contact with the perimeter of an electrode according to anembodiment of the present invention;

FIG. 17G shows an exploded view of a single cell module with the busbarsin contact with the perimeter of an electrode according to an embodimentof the present invention;

FIGS. 18A-18J show a breakout of each layer of an example single cellmodule with busbars providing near full perimeter contact with anelectrode layer according to an embodiment of the present invention;

FIG. 18K is an exploded view of an example single cell module withbusbars providing near full perimeter contact with an electrode layeraccording to an embodiment of the present invention;

FIG. 19 is a cross-sectional view illustrating an example multi-junctioncell module according to an embodiment of the present invention;

FIGS. 20A-20E illustrate current-density versus voltage plots forexample multi-junction cell modules with different numbers of junctionsand cell areas;

FIG. 20F is a table showing performance parameters of the examplemulti-junction cell modules with different numbers of junctions and cellareas; and

FIG. 21 is an exploded view illustrating a fixture assembly configuredto interface with a single cell module as described herein.

DETAILED DESCRIPTION OF THE INVENTION

The inventors have determined that transparent electrode layersgenerally have a higher sheet resistance than nontransparent electrodes.The addition of series resistance in photovoltaic (PV) modules may causea higher power loss and may significantly reduce the overall efficiencyof the PV modules. In conventional PV technologies, the reduction ofseries resistance is of significant importance to obtaining the highestperformance and is achieved through a number of approaches that include,but are not limited to, patterning the module into subcells withoptimized dimensions, use of highly conductive opaque conductiveelectrodes, and the deposition of highly conductive bus bars over themodule area. These optimizations enable conventional technologies tolimit series resistance but different processes and methodologies mustbe used when fabricating transparent photovoltaic modules, inparticular, PV modules with large active areas (and thus large seriesresistance). Accordingly, embodiments of the present invention reducethe series resistance of the PV modules or otherwise reduce power lossto improve the overall efficiency of the PV modules.

As used herein, the term transparent means at least partial transmissionof visible light. In general, power output of transparent PV modules canbe reduced by the introduction of an additional series resistance. Suchseries resistance can arise from the inherent sheet resistance oftransparent electrodes that are necessary in transparent PV modules andmodules to allow light transmission into the photoactive semiconductorsand also transmission through the module itself. Conventional PVtechnologies reduce the series resistance through highly conductiveopaque metal electrodes, highly conductive opaque busbars over themodule area, and patterning the module into subcells with optimizeddimensions to reduce the operating current. Application of opaqueelectrodes and patterned opaque metal busbars to a transparent modulearea causes a tradeoff between good aesthetics (transparency) andperformance (higher series resistance) and these approaches are lessdesirable for transparent PV modules. Further, transparent PV modulestypically use electrode materials that have a higher resistance thanconventional opaque materials resulting in a tradeoff in increasing themodule area with increasing the series resistance (reduced moduleperformance).

Finally, patterning the module area into sub cells can lead to visualfeatures that may be undesirable for transparent PV modules. The modulesdiscussed herein utilize alternative approaches to reducing orminimizing series resistance additions and module efficiency losses fortransparent PV modules when good aesthetics are required and twotransparent electrodes must be employed. Such modules can be used in avariety of applications including rigid and flexible computer displayscreens used in a desktop monitor, laptop or notebook computer, tabletcomputer, mobile phone, e-readers, and the like. Other applicationsinclude watch faces, automotive and architectural glass includingsunroofs and privacy glass. The photovoltaic modules may be used foractive power generation, e.g., for completely self-powered applications,and battery charging (or battery life extension).

The embodiments described herein use various PV arrangements includingelectrodes, busbars, and contacts. In some embodiments, electrodes canbe electrical conductors used to make contact with a nonmetallic part ofa circuit. The electrode can form part of an active area of a module andcan extend outside of the active area to connect with a busbar orvarious types of contacts. In some embodiments, electrodes can have ahigher resistance than busbars and/or contacts. Sheet resistances ofelectrodes can be in the mΩ/sq range for opaque electrodes and rangefrom 1 Ω/sq-100 Ω/sq for transparent electrodes. Electrodes can befabricated using physical vapor deposition (PVD) techniques such asthermal evaporation, electron beam physical vapor deposition (EBPV),sputter deposition, or the like. Opaque electrode embodiments caninclude metals such as aluminum, silver, or gold, which can be depositedby PVD, generally ranging from 20 nm-300 nm in thickness. In someembodiments, transparent electrodes can be fabricated by PVD and includethin metal layers such as aluminum, silver, or gold (4 nm-12 nm) coupledwith organic (e.g. small molecules) or inorganic dielectric layers(e.g., metal oxides) over a wide range of thicknesses (1 nm-300 nm) toimprove optical transmission. Transparent electrodes can also befabricated by PVD of conductive oxide materials such as indium tin oxide(ITO), aluminum zinc oxide (AZO), antimony tin oxide (ATO), fluorine tinoxide (FTO), and indium zinc oxide (IZO). Transparent electrodes canalso be made from different metal nanostructures such as silvernanowires and nano-cluster that can be deposited using a variety ofsolution-deposition techniques (spin-coating, blade-coating,spray-coating). Transparent electrodes may also be made from graphene orcarbon nanotube layers. Metals can be structures or patterned to formporous grid or network structures to make transparent electrodes.

In some embodiments, busbars can be conductors that provide pathways totransport current between electrodes and contacts. Busbars can be ametallic bar or strip and can also be deposited and patterned to formdifferent pathway patterns. In some embodiments, busbars can be opaqueand reside outside of the active area of the module. Busbars can havelower resistance than electrodes and higher resistance than contactcomponents. Busbars can be fabricated from various materials, including,for example thin metal layers of Ag or Al, conductive silver pastes orepoxies, and the like. Resistance through busbars can depend on thematerial, the material thickness, and the lateral layout and dimensionsof the busbar (e.g., width and length of busbar between electrode andcontact point). In some embodiments, busbar can include metal filmlayers of silver, aluminum, gold, copper, or other highly conductivemetals deposited using different PVD techniques, with thicknesses over100 nm to lower resistance. Busbars can be fabricated using conductivepastes or epoxies, which can be an emulsion of silver in solvent or anepoxy medium. Conductive pastes or epoxies can be patterned manually orusing techniques such as ink jet printing or screen printing. Substratesmay be pre-printed with patterned busbars or busbars may be added duringor after the other PV module layers.

In some embodiments, as discussed further below, the busbars and orelectrode 450 can be in electrically coupled to one or more contacts.Contacts can refer to the points on a PV module where electricalconnection is made between the module's electrodes or busbars to anoutside circuit. Contacts to a module can be temporary, semi-permanent,or permanent. In some embodiments contact components, such as wires,pins, ZEBRA connectors, etc. can be very low resistance (<1Ω, preferablyin the mΩ range across the length of the component). Resistance candepend on the type of connector and the dimension (e.g. the length of awire or the conductive material in a ZEBRA connector). Contacts can beconnected to electrodes or busbars and transport charge to circuits orother components used to connect the module for testing or powering aload.

In various embodiments of the present invention there are many potentialpoints for reducing charge loss in a PV module. In certain embodiments,the design, the materials, the configurations, and the components can bevaried to minimize different resistance losses. In general, thefollowing resistance losses can be considered: losses from top andbottom electrode resistance, losses from electrode to busbar orelectrode to contact resistance, losses from busbar resistance, lossesfrom busbar to contact resistance, losses from contact components, andlosses from other electrical connections and components.

According to embodiments of the present invention, the contactresistance between electrode to busbar/contact or busbar to contact canbe relatively small. Losses in contact components and other electricalcomponents can be negligible in comparison to electrode and busbarresistances. In some embodiments, the primary resistive loss can be froman electrode resistance, followed by a busbar resistance. The power lossfrom resistance can depend on the electrode and busbar electricalproperties as well as the dimensions and geometry of the cell andcontact layout.

FIG. 1A shows a schematic of an active area of a photovoltaic cellaccording to an embodiment of the present invention. The photovoltaiccell 100 can be used to illustrate the relationships between moduleparameters and power loss for a single cell with simple contactconfigurations. The photovoltaic cell 100 includes an active area 110with a height, h, 112 and a width, w, 114. The active area can includeone or more electrodes, one or more active layers, and one or moreinterconnects in a tandem structure. In some embodiments, one or moreelectrodes can be transparent. The photovoltaic cell 100 also includes afirst busbar 120 along a first side 116 of the active area 110. In theillustrated embodiment, the power loss from sheet resistance of anelectrode can generally be calculated starting with Equation (1), thegeneral formula for power loss:

P _(loss) =I ² R  (1)

Current is generated throughout the cell active area 110. Resistivelosses will not be equal for all charge generated because charge isgenerated at different distances away from the first busbar 120.Equations (2-5) integrate the power loss over y 130 to relate power lossto the width 114 of the active area 110.

$\begin{matrix}{{dP}_{loss} = {I^{2}{dR}}} & (2) \\{{dR} = {\frac{\rho}{h}{dy}}} & (3) \\{{I(y)} = {Jhy}} & (4) \\{{P_{loss} = {{\int{{I(y)}^{2}{dR}}} = {{\int_{0}^{w}\frac{J^{2}h^{2}y^{2}\rho \; {dy}}{h}} = \frac{J^{2}h\; \rho \; w^{3}}{3}}}},} & (5)\end{matrix}$

where ρ is the resistivity of the electrode.

The power generated by the photovoltaic cell 100 can be calculated usingEquation (6):

P _(gen) =J _(MP) whV _(MP),  (6)

where J_(MP) is the current density at the maximum power point andV_(MP) is the voltage at the maximum power point.

The percentage of power loss is then the lost power divided by thegenerated power:

$\begin{matrix}{P_{\% \mspace{14mu} {loss}} = {\frac{P_{loss}}{P_{gen}} = {\frac{\rho \; w^{2}J_{MP}}{3\; V_{MP}}.}}} & (7)\end{matrix}$

Sheet resistance (Rsh) of the electrode is directly proportional toresistivity of the electrode and can be used as a metric forcharacterizing electrodes. In other embodiments resistivity can be usedas a metric for characterizing electrodes. In some embodiments, anattached circuit can control the voltage and/or current to operate atthe maximum power point. Operating the photovoltaic cell current andvoltages at the appropriate levels can maximize power extraction underall conditions.

The changes to various module properties can affect power loss in thephotovoltaic cell 100. For example, as shown in Equation (7), thepercent power loss scales with the square of the cell width, linearlywith the current, and inversely with the voltage. Some embodimentsimplement a photovoltaic cell design with low current and high voltageto minimize performance drop in large photovoltaic cells 100.

FIG. 1B shows the effect of active area sheet resistance on resistivepower loss. The results illustrated in FIG. 1B are based on an assumedcurrent density at maximum power point, J_(MP), of 3 mA/cm² and V_(MP)of 1.2 V. The x-axis 152 represents cell width w 114. The y-axis 154represents the resistive power loss percentage. The plot 150 includes aplurality of curves 156, each curve associated with a different sheetresistance value in f/sq. The value associated with each curve issummarized in the legend 158. FIG. 1B illustrates that withoutmodification, as the width w 114 of the photovoltaic cell 100 increases,resistive power losses will continue to increase.

In some embodiments, sheet resistance of a transparent electrode can bethe limiting factor in module area scaling. Embodiments of the presentinvention utilize transparent electrodes that provide a combination ofhigh conductivity (i.e., low sheet resistance) and low absorptive loss(i.e., low absorption coefficient).

Starting with the general formula for power loss, Equation (8) providesthat:

P _(loss-busbar) =I ² R  (8)

If all the charge generated is being transported by a busbar 120 to acontact point on either end, the power losses in the busbar can becalculated by integrating over the length L in the x-direction 136:

$\begin{matrix}{\mspace{79mu} {{dP}_{{loss}\text{-}{busbar}} = {I^{2}{dR}}}} & (9) \\{\mspace{79mu} {{dR} = {\frac{\rho_{busbar}}{w_{f}}{dx}}}} & (10) \\{\mspace{79mu} {{I(x)} = {Jwx}}} & (11) \\{P_{{loss} - {busbar}} = {{\int{{I(x)}^{2}{dR}}} = {{\int_{0}^{L}\frac{J^{2}w^{2}x^{2}\rho_{busbar}\; {dx}}{w_{f}}} = \frac{\rho_{busbar}J^{2}w^{2}L^{3}}{3\; w_{f}}}}} & (12)\end{matrix}$

The total generated power can be calculated as:

P _(gen-busbar) =J _(MP) wLV _(MP)  (13)

and the percentage of power loss P_(%loss-busbar) is then the lostpower, P_(loss-busbar) divided by the generated power, P_(gen-busbar):

$\begin{matrix}{P_{{\% \mspace{14mu} {loss}} - {busbar}} = {\frac{P_{{loss}\text{-}{busbar}}}{P_{{gen}\text{-}{busbar}}} = \frac{\rho_{busbar}J_{MP}{wL}^{2}}{3\; w_{f}V_{MP}}}} & (14)\end{matrix}$

Equation (14) shows that power loss is directly proportional to busbarlength L 134 squared and the current, J_(MP). The power loss isinversely proportional to the voltage. Some embodiments can beconfigured to operate with low current and high voltage to minimizeperformance loss due to electrode resistance. In some embodiments,busbars will be made from low resistance materials that result in anegligible power loss in comparison to losses attributed to moduleelectrode resistance.

In some embodiments, a second busbar (not illustrated) can be fabricatedon another edge of the active area 110. In particular embodiments, thesecond busbar can be in electrical contact with a second side 118 of theactive area 110 opposite to the first side 116. In this embodiment, themaximum width that a charge must travel becomes halved and results in aneffective width of w/2. Substituting the effective width of a two busbarphotovoltaic cell 100 for w in the result of Equation (5) causes thepower loss over the active area 110 to become:

$\begin{matrix}{P_{loss} = {{\int{{I(y)}^{2}{dR}}} = {{\int_{0}^{w}\frac{J^{2}h^{2}y^{2}\rho \; {dy}}{h}} = \left. \frac{J^{2}h\; \rho \; w^{3}}{3}\rightarrow\frac{J^{2}h\; \rho \; w^{3}}{24} \right.}}} & (15)\end{matrix}$

The reduced charge travel distance results in a decrease in the powerloss due to electrode resistance. The source of the decreased power lossis the increased denominator as a result of the effective width, w/2, inthe last step of Equation (15). Accordingly, in a two busbarphotovoltaic cell the percent power loss becomes:

$\begin{matrix}{P_{\% \mspace{14mu} {loss}} = {\frac{P_{loss}}{P_{gen}} = \left. \frac{\rho \; w^{2}J_{MP}}{3\; V_{MP}}\rightarrow{\frac{\rho \; w^{2}J_{MP}}{12\; V_{MP}}.} \right.}} & (16)\end{matrix}$

Thus, the percent power loss in a two busbar configuration is reduced to25% of the power loss shown in Equation (7). As described herein,various embodiments of the present invention reduce the charge traveldistance to reduce the percent power loss accordingly.

In conventional PVs, the back electrode is typical an opaque highlyconductive metallic electrode. However, transparent PV embodimentsrequire both the top and bottom electrode to be transparent, and highlyconductive metal electrode cannot typically be used. Due to theincreased sheet resistance of transparent electrodes compared to opaquemetal electrodes, this can increase resistive power losses observed fortransparent PVs.

One approach to minimize the impact of increased sheet resistance fromthe transparent electrodes is to incorporate metallic busbars over theactive area. These can be printed to cover portions of the active modulearea, but can create visible line features that change the viewingappearance and reduce the overall transmission through the module.Typical arrangements of metal grids within the active area can includemacroscopically defined busbar arrays defined over a few centimeters,smaller grid arrays defined as either hexagonal or striped, and thelike. In all cases the grid array obstructs the field of view.

A second approach to minimizing power loss is to subdivide the modulearea into a series-integrated sub cells. Subdividing the module areareduces the charge travel distance in each cell, and series integrationallows the PV to run at a low current (that of a single sub cell) and ahigh voltage (summation of sub cell voltages) to help minimizingresistive power losses. Each sub-cell comprises a top electrode, anactive layer, and a bottom electrode.

FIG. 2A shows an example of a monolithic series integrated solar cell200 with 8 sub-cells in series. FIG. 2B shows an expanded plan view of aportion of the monolithic series integrated solar cell illustrated inFIG. 2A. In FIG. 2B, a first bottom electrode 210 separated from asecond bottom electrode 212 by an electrical isolation line 214 areshown. In some embodiments, one or more of the first and second bottomelectrodes can be a highly conductive metallic electrode. Each bottomelectrode is in electrical contact with an active layer. In someembodiments the photovoltaic material active layer can be composed ofcadmium telluride, silicon, organic semiconductors, and the like. InFIG. 2B, the first bottom electrode 210 is in electrical contact with afirst active layer 220 and the second bottom electrode 212 is inelectrical contact with a second active layer 222. Each cell can includea top electrode in electrical contact with an active layer. In FIG. 2B,the first active layer 220 can be in electrical contact with a first topelectrode 230 and the second active layer 222 can in electrical contactwith a second top electrode 232.

FIG. 2C shows a cross-section of the architecture at line 2C in FIG. 2A.The cross-section view shows how the individual cells can be connectedin series. First, the electrical isolation line 214 can be seen betweenthe first bottom electrode 210 and the second bottom electrode 212. Thefirst active layer 220 is shown in electrical contact with the firstbottom electrode 210 and the first top electrode 230. A gap 240 betweenthe first active layer 220 and the second active layer 222 allows thefirst top electrode 230 to contact the second bottom electrode 212between sub-cells to create a series connection between cells.

Sub-cell optimization of photovoltaic cells can be used to limit serialresistance with organic photovoltaic modules. In some embodimentscomprising an organic photovoltaic module (OPV), an opaque OPV can befabricated. In embodiments with an opaque OPV, one of the electrodes,for example the bottom electrode 210, can be opaque and fabricated froma highly conductive metallic electrode while the second, for example,top electrode 230, can be made from a transparent typicallyless-conductive electrode material. In embodiments comprising an opaqueOPV an array of metallic bus bars can be printed onto the OPV module toreduce the series resistance.

Sub-cell module configurations can reduce resistive power losses, butresults in area loss in the interconnect regions and also result invisible patterning which may be undesirable for transparent PVapplications. In some embodiments the viewing appearance can also becompromised by the electrical isolation lines 214 within the activearea. The addition of wider electrical isolation lines 214 increasesdesign and fabrication tolerance, but wider lines have greatervisibility and, being inactive, cause a loss in the overall currentgenerating area and reduce module efficiency.

In some embodiments, fabricating a single cell module 300 versus amonolithic series integrated solar module 200 eliminates the patterninglines present in the central active area of the module. For manyapplications of transparent PVs, it is desirable for this central regionto be transparent and free of visual patterns. An example of anundesirable patterning line in the central region is illustrated byelectrical isolation line 214 in FIG. 2C.

Patterning lines can also include the edges of electrodes and activelayers that are either inside or outside of the central module area, butrequire fabrication considerations as these may include potentialelectrical shorting locations that can cause decreased performance orprevent the module from functioning. The patterning lines can befabricated using shadow masking, laser scribing, or other techniques inorder to isolate bottom and top electrodes as well as remove materialfrom the active layers to provide contact pathways. FIGS. 3A and 3Billustrate the reduced number and length of patterning lines used in asingle cell module versus a series integrated module. FIG. 3A is a planview of a single cell module 300. The patterning lines 310, which areassociated with edges of features in the module, indicate regions of thesingle cell module 300 where potential shorting locations exist that cancause decreased performance or prevent the module from functioning. Insome embodiments, the single cell module 300 will have a number ofpatterning lines associated with the perimeter of the top electrode 320and the active layer 330.

FIG. 3B is a plan view of a series integrated module 350 with 8sub-cells. There are patterning lines 310 associated with eachindividual sub-cell in the series integrated module 350. In theintegrated module illustrated in FIG. 3B, patterning lines areassociated with the perimeter of the active area of the module and aredisposed within the active area of the module. In contrast with thesingle cell module 300, the series integrated module 350 has 2.5 timesmore patterning lines 310. The reduced number of patterning lines 310 inthe single cell module 300 can provide several benefits includingreducing the complexity of the contacting scheme; implementingnon-standard and non-rectangular application geometries; reducing themask edge contact per area; reducing dead areas that do not contributeto power generation; and improved aesthetics.

While sub-cells can be used to decrease the travel distance for chargesgenerated in the active area of a module, several techniques can beapplied to reduce the charge travel distance of single cell modules. Forexample, parameters that can be adjusted to reduce the charge traveldistance include the aspect ratio of the module geometry, theresistivity of the electrode the contact, and busbar materials and thelike.

FIGS. 4A-D show the direction of charge travel in a single cell modulewith an increasing number of contacts in four different contactconfigurations. The various configurations illustrate the contact edgeimpact on charge travel distance with reference to just one of the twoelectrodes utilized in a PV cell. FIGS. 4A-D illustrate only a singleelectrode for simplicity, but such configurations can be overlaid with aphotovoltaic active material layer and a second counter electrode. Inpractice, contact and busbar patterns can be used and optimized for eachelectrode. For example, both electrodes could have full perimetercontact for optimized charge extraction or the amount of perimetercontact could be varied between the top and bottom electrodes to havemore contact with the higher resistance electrode to better matchresistance losses.

FIG. 4A shows a first contact configuration 401 that includes a firstbusbar or contact 410 for an electrode 450. FIG. 4B shows a secondbusbar or contact configuration 402 that includes the first contact 410and a second contact 412. FIG. 4C shows a third busbar or contactconfiguration 403 that includes the first contact 410, the secondcontact 412, and a third contact 414. FIG. 4D shows a fourth busbar orcontact configuration 404 that includes first contact 410, the secondcontact 412, the third contact 414, and a fourth contact 416. In eachconfiguration, the charge travel distance can depend on the number andlocation of contacts in electrical contact with the electrode 450.

The embodiments shown in FIGS. 4A-D illustrate how current is beinggenerated throughout the entire active area of the module and needs totravel to contact points on the edge, or periphery of the electrode 450.The locations of contacts and busbars placed around the perimeter of theelectrode 450 can be adjusted to provide the shortest travel distancefor charge to travel at various locations within the cell. For example,in the first configuration 401, referring to FIG. 4A, all charges in theactive area of the electrode 450 travel in a first direction 420 toreach the first contact 410. In this configuration, charges near theopposite edge 452 of the electrode 450 travel the entire distance acrosselectrode 450 to reach the first contact 410. This configuration resultsin a higher sheet resistance and increased power loss. In the secondcontact configuration 402, referring to FIG. 4B, the second contact 412enables charges on the electrode 450 to travel in a second direction422. As discussed above, the second contact 412 reduces the effectivewidth and charges can travel shorter distances resulting in a decreasedpower loss. In a configuration with two contacts such as the secondcontact configuration 402, the longest distance any charge must travelis now half of what it was with a single contact such as the firstconfiguration 401. The third contact configuration 403, referring toFIG. 4C, and the fourth contact configuration 404, referring to FIG. 4D,provide a third direction 424 and a fourth direction 426 to furtherreduce the travel distance for charges on the electrode 450. In someembodiments, having full perimeter contact can minimize power loss forany single cell without adding internal busing or other design elements.With full perimeter contact, all current pathway distances to an edgecontact are minimized.

The electrode 450 can be an electrical conductor used to make contactwith a nonmetallic part of a circuit, for example, organic photovoltaicmaterial layer. The electrode 450 forms part of the active area of amodule and can extend outside of the active area to connect with abusbar or various types of contacts (e.g. 410, 412, 414, 416). In someembodiments, sheet resistances of electrodes are generally in the mΩ/sqrange for opaque electrodes and usually range from 1 Ω/sq-100 Ω/sq fortransparent electrodes. In some embodiments, electrode 450 can have ahigher resistance than busbars and/or contacts 410, 412, 414, 416.Electrode 450 can be fabricated using physical vapor deposition (PVD)techniques such as thermal evaporation, electron beam physical vapordeposition (EBPV), sputter deposition, or the like.

The square single cell module configurations shown in FIGS. 4A-4D areexemplary and modules can be varied height, width, and shape. In someembodiments, the contact configuration can be determined based on therequirements of a particular application. Any of the single cell modulesillustrated in FIGS. 4A-4D can be used in, for example, fitnesstrackers, pulse tracker bands, watches, fitness armbands with a chargingcapability, glasses requiring a localized power source, wearableheads-up displays, wearable LED jewelry, medical monitoring patches,built-in cellphone emergency chargers, electronic labels, and the like.In some embodiments, the size range of the single cell module can be 2-5cm across. Single cell modules can be made for even larger sizes butcharge travel distance will increase. Generally, a transparent singlecell module can be integrated into an information display system togenerate charge for the associated system. The limitation on size willdepend on the power requirements for the intended application and themodule stack architecture used.

FIG. 5 shows a table with dimensionless ratios of charge traveldistances for different perimeter contact configurations. Table 500includes calculations from a 1000-point mesh in an x-direction and ay-direction. A distance to the nearest electrode is calculated for eachpoint and the distances are summed for all points in the mesh. Thenumber shown in the table for each configuration is the ratio of thesummed distances of the points for a given configuration to the summeddistances of the points for the configuration with a single contactalong one full edge. Table 500 shows the reduction in point distancesfor each busbar configuration as a dimensionless ratio for comparingdifferent electrode configurations to a baseline, one full edge contactconfiguration.

FIG. 6A is a cross-sectional view of an example single cell modulehaving two contacts according to an embodiment of the present invention.The single cell module 600 includes a first electrode layer 610, acontact point 614 on a first electrode pad 612, one or more photovoltaicmaterial layers 620, a second electrode layer 630, and a contact point634 on a second electrode pad 632. Since PV cells can be fabricatedusing a layering process, starting with a bottom layer and addingelements until a top layer is reached, references to first and secondelements of a cell can also be referred to as bottom and top elements.For purposes of clarity, references herein utilize the bottom/topnomenclature in reference to various figures, but it will be appreciatedthat alternative fabrication processes and cell designs can be utilizedin which right/left nomenclature could be appropriate. Accordingly, thebottom/top nomenclature utilized here is not intended to limit the scopeof the present invention and is utilized for first/second nomenclaturemerely for purposes of clarity.

In some embodiments, a central transparent area 650, which can also bereferred to as an active area, can include the overlapping portions ofthe top electrode 630, the one or more photovoltaic material layers 820,and the bottom electrode 610. The single cell module 600 shows a methodcontacting a cathode and an anode using a single point of contact. Inthe embodiment shown in FIGS. 6A and 6B, the contacts arenon-interdigitated and non-overlapping (each described further below).

FIG. 6B is a plan view of an example single cell module having twocontacts according to an embodiment of the present invention. In someembodiments, electrical contact between the bottom electrode 610 and thecentral transparent area can extend along a first side 652 of thecentral transparent area 650 and electrical contact between the topelectrode 630 and the central transparent area can extend along a secondside 654 of the central transparent area 650. In some embodiments, thecontact point 614 formed on the first electrode pad 612 and contactpoint 634 formed on the second electrode pad 632 can be fabricated usinglow resistance materials, which can also be used on busbars or othercontacts as described herein.

FIG. 7 shows dimensionless ratios of charge travel distances fordifferent two-contact configurations of a single cell module. Theconfigurations contain different designs for two contact layouts wherethere is one contact or busbar for each electrode on a square singlecell module. The corner contacts configuration 704 and the C-shapecontact configuration 706 are compared to the first configuration 702where there is a single contact for each electrode on opposing sides.The table 700 shows the travel distance is reduced when comparing thecorner contacts configuration 704 to the first configuration 702. Thetable 700 shows the travel distance can be reduced further whencomparing the C-shape contact configuration 706 to the firstconfiguration 702. In some embodiments, the C-shape contactconfiguration can be comprised of a c-shaped conductive material region.

FIG. 8A is a cross-sectional view of an example single cell module withinterdigitated contact pads according to an embodiment of the presentinvention. The single cell module 800 can include a bottom electrode 810including a bottom surface 811 and an opposing top surface. A contiguouscentral region 814 of the bottom electrode 810 is electrically coupledto a set of electrode pads surrounding the contiguous central region. InFIG. 8A, bottom electrode pad 812 is illustrated as an example of theset of the bottom electrode pads.

In some embodiments, the bottom electrode 810 can also include one ormore isolated electrode pads 832 that are electrically isolated from thecontiguous central region 814 and the set of electrode pads representedby bottom electrode pad 812. As illustrated in FIG. 8A, one or more lowresistance contact points 816 and 836 can be formed on the bottomelectrode pads 812 and the isolated electrode pads 832.

In some embodiments, the single cell module 800 can include one or morephotovoltaic material layers 820 including a top surface 821 and anopposing bottom surface. A contiguous central region 822 of thephotovoltaic material layer is illustrated. In some embodiments, thesingle cell module 800 can also include a top electrode 830 having a topsurface 831 and an opposing bottom surface. A contiguous central region836 of the top electrode 830 is electrically coupled to a set ofelectrode pads surrounding the contiguous central region. In FIG. 8A,top electrode pad 838 is illustrated as an example of the set of the topelectrode pads. As described herein, the electrode pads extending from,or disposed outside the periphery of the contiguous central region,provide for electrical contact to the contiguous central region and thecontact points electrically coupled to the electrode pads. Referring toFIG. 8A, the top electrode 830 can be electrically coupled to isolatedelectrode pad 832.

Referring once again to FIG. 8A, a central transparent area 850 of thesingle cell module 800 can be defined by the overlap of the contiguouscentral regions 814, 822, and 836 of the bottom electrode, photovoltaicmaterial layers, and the top electrode, respectively. In someembodiments, the central transparent area 850 of the single cell module800 can be transparent to visible light while absorbing light in theultraviolet and/or infrared portions of the spectrum.

FIG. 8B is a plan view of an example single cell module withinterdigitated contact pads according to an embodiment of the presentinvention. In some embodiments, electrical contact to the bottomelectrode 810 and the top electrode 830 can be implemented usingmultiple interdigitated pairs of electrode pads 812/832 havinginterdigitated pairs of contact points 840 on all edges for both cathodeand anode, where the cathode and the anode correspond to the bottomelectrode 810 and the top electrode 830. A single pair of interdigitatedcontact points 840 can be contact points formed on an isolated electrodepad 832 coupled to the top electrode 830 and a bottom electrode pad 812coupled to the bottom electrode. In some embodiments, interdigitatedlycan describe a pattern of alternating isolated electrode pads 832coupled to the top electrode 830 and bottom electrode pad 812.

FIG. 8B shows an example with four pairs of electrode pads for thecathode and anode on all four sides of a square single cell module 800.For example, isolated electrode pads 832 are electrically coupled to thetop electrode pads 838 extending from the periphery of the contiguouscentral region of the top electrode 830 and bottom electrode pads 812are electrically coupled to the contiguous central region of the bottomelectrode 810. Both isolated electrode pads 832 and bottom electrodepads 812 can have a low resistance contact point 816 formed thereon. Thecontact points can extend from electrode layer, be flush with theelectrode layer, or recessed. Accordingly, in FIG. 8B, 16 total contactpoints 816 are provided for each electrode, with eight total contactpoints (including contact points for both electrodes) on each edge ofthe single cell module 800, resulting in four pairs of interdigitatedcontact points 840 per side. The number of electrode pads and contactpoints can be increased or decreased as needed.

FIGS. 8C-8N show a breakout of each layer of the interdigitated singlecell module shown in FIG. 8B. FIG. 8C shows a first layer of a singlecell module. In some embodiments, the first layer comprises a bottomelectrode 810. The bottom electrode 810 can include a contiguous centralregion 814 that has a periphery 813 that extends out to four bottomelectrode pads 812 on each edge of the module. The bottom electrode pads812 can provide a location for contact points 860 on the bottomelectrode 810. In some embodiments, the bottom electrode 810 can includeone or more isolated electrode pads 832 that are electrically isolatedfrom the contiguous central region 814 and the bottom electrode pads812. In some embodiments, the isolated electrode pads 832 can beinterdigitated with the bottom electrode pads 812 (e.g., four on eachside of the module). The one or more isolated electrode pads 832 cansupport contact points 860 electrically coupled to the top electrode 830and, along with bottom electrode pads 812, form electrode pad pairs inan interdigitated manner. The four isolated corner pads that do notconnect to the cell can be fabricated to provide even color and opticaleffects across the substrate. A corner mark 818 illustrated on one ofthe four isolated corner pads can help to orient the substrates duringprocessing and acts as a visual guide to the top and bottom side of thesubstrate. FIG. 8D shows a first partially manufactured single cellmodule 801 comprising the first layer.

FIG. 8E shows a second layer of a single cell module. The second layercan include one or more photovoltaic material layers 820 and can bepositioned above the bottom electrode central region 814. Thephotovoltaic material layers 820 can include a central transparent area822 corresponding to the active area for the module. Portions of thephotovoltaic material layers 820 can extend beyond the periphery 813 ofthe contiguous central region 814 to cover a portion of both the bottomelectrode pads 812 and the isolated electrode pads 832. The photovoltaicmaterial layers 820 can act as electrical insulation to impedeelectrical contact between a top electrode 830 and bottom electrode 810.FIG. 8F shows a second partially manufactured single cell module 802comprising the first and second layers formed with the bottom electrodecentral region 814 and the active area central region 822 substantiallyaligned.

FIG. 8G shows a third layer of a single cell module. The third layer caninclude the top electrode 830. The top electrode 830 can be formed ontop of the one or more photovoltaic material layers 820 with a topcentral region 836 that can correspond to the active area of the singlecell module. The top electrode 830 can include one or more top electrodepads 838 that extend out from the top central region 836 to connect tothe optional one or more isolated electrode pads 832 that are disposedadjacent the edge of the substrate. FIG. 8H shows a third partiallymanufactured single cell module 803 comprising the first, second, andthird layers formed with the bottom electrode central region 814, theactive area central region 822, and the top central region 836substantially aligned.

FIG. 8I shows a fourth layer of a single cell module. The fourth layercan include cavity glass 840 or other glass or barrier materials thatcan be placed and/or fabricated over the module layers. The cavity glass840 can be formed to leave one or more of the electrical elements, suchas the one or more isolated electrode pads 832 and the bottom electrodepads 812, exposed. FIG. 8J shows a fourth partially manufactured singlecell module 804 comprising the first, second, third, and fourth layersformed with the bottom electrode central region 814, the active areacentral region 822, the top central region 836 and the cavity glass 840substantially aligned.

FIG. 8K shows a fifth layer of a single cell module. The fifth layer caninclude a size aperture 850. The size aperture 850 can be used to blocklight outside the desired active area size. FIG. 8L shows a fifthpartially manufactured single cell module 805 comprising the first,second, third, fourth, and fifth layers formed with the bottom electrodecentral region 814, the active area central region 822, the top centralregion 834, the cavity glass 840, and the size aperture 850substantially aligned.

FIG. 8M shows a sixth layer of a single cell module. The sixth layer caninclude one or more low resistance contact points 816. The one or morecontact points 816 can be formed on each individual bottom electrode pad812 and isolated electrode pad 832. Connections to the single cellmodule from other devices can be made using the one or more contactpoints 816 on each edge of the module. FIG. 8N shows a fullymanufactured single cell module 806 comprising the first, second, third,fourth, fifth, and sixth layers formed with the bottom electrode centralregion 814, the active area central region 822, the top central region834, the cavity glass 840, the size aperture 850, and the one or morecontact points substantially aligned.

FIG. 8P shows an exploded view of the single cell module according to anembodiment of the present invention. The single cell module includes abottom electrode 810, one or more photovoltaic material layers 820, atop electrode 830, cavity glass 840 or other barrier material, a sizeaperture 850, and a particular arrangement of one or more contact points860. It should be appreciated that the specific layers illustrated inFIG. 8P provide a particular arrangement of a single cell module withinterdigitated contacts according to an embodiment of the presentinvention. Other layers or contacts may also be formed thereon accordingto alternative embodiments. Moreover, the individual module layers andcomponents illustrated in FIG. 8P may include multiple sub-layers thatmay be formed and/or fabricated in various arrangements as appropriateto the individual module. Furthermore, additional layers or componentsmay be added or existing layers or components may be removed dependingon the particular applications. One of ordinary skill in the art wouldrecognize many variations, modifications, and alternatives.

Power losses from resistance (e.g., in the electrodes, busbars, andcontact points) can be related to the level of the current passingthrough the resistive features, the dimensions of the resistivefeatures, and the resistivity of the features. In some embodiments, thematerials and architecture and/or the geometry can be designed tominimize the current and reduce power losses. In some embodiments,components of the PV module can be designed to operate at an increasedvoltage and lower current to minimize losses.

FIG. 9 shows dimensionless ratios of charge travel distances fordifferent interdigitated contact configurations. The first column 901shows the different numbers of contacts in various embodiments for eachelectrode on each of the 4 sides of a square single cell module. Thesecond column 902 shows the dimensionless ratio of charge traveldistances for each embodiment in the first column 901. The third column903 shows a plan view for each embodiment in the first column 901. Thefigures in the third column illustrate electrode details for eachembodiment. Using row 930 column 903 as a reference, the black regionson the plan view illustrate the top electrode geometry. The white gaps932 illustrate the contact points for the bottom electrode and theprotruding black regions 934 illustrate the contact points for the topelectrode. The last row of table 900 shows a comparison for a fullycontacted perimeter for both top and bottom electrodes (the minimum sumof point distances that can be achieved with a top and bottom electrodeconfiguration).

The number of interdigitated contact pairs can be adjusted to optimizethe sheet resistance of both the top and bottom electrodes. In someembodiments, increasing the number of interdigitated contact pairs canreduce the sheet resistance of the electrodes and decrease the powerlosses when scaling the single cell modules to larger areas. Increasingthe number of contact pairs reduces the average charge travel distanceand causes the percent power loss to decrease. In some embodiments,increasing the number of interdigitated contact pairs can maximize lowresistance edge coverage for the electrodes (either contact point orbusbar). Maximizing the edge coverage in some embodiments can includemaximizing the points of contact or forming a connection to a busbararound the full perimeter. In some embodiments, a full perimeter contactto a low resistance busbar for both electrodes can minimize the powerloss. An alternative to full perimeter contact is to form interdigitatedcontacts for both electrodes around the perimeter of the single cellmodule active area.

Referring to FIGS. 8A and 8B, connection must be made with both thebottom electrode 810 and the top electrode 830 (the anode and cathode)to be considered a contact for the purposes determining thedimensionless ratio of charge travel distances. A connection includes afirst contact point with the anode and a second contact point with thecathode. The second column 902 shows ratios of point distances, or thedistance individual charges must travel from any point on the activearea. Table 900 includes contact points for both top and bottominterdigitated electrodes. All the configurations in table 900 are for a4-edge perimeter contact with varying numbers of interdigitated contactson each side. The first row 910 with 0.25-contacts per side and thesecond row 920 with 0.5-contacts per side are equivalent contactnumbers. The configuration for the first row 910 with 0.25-contacts perside can include a left side that is a bottom electrode contact pointand a right side that is a top electrode contact point. The two contactpattern shown in the first row 910 includes only one contact point perelectrode. The first row 910 is therefore used as the basis ofcomparison to determine the dimensionless ratio to characterize chargetravel distances for all other configurations.

In some embodiments, the single cell module can include 0.5-contacts perside as shown and described in the second row 920. Embodiments with0.5-contacts per side can include left and right side bottom electrodecontact points and top and bottom side top electrode contact points.Embodiments described herein can form a plurality of contacts orcontinuous contact on each side of a single cell module and can furtherreduce charge travel distance for various configurations. For example,using a 1000-point mesh in both x and y, the sum of point distances tothe nearest electrode in each configuration in column 901 of table 900is divided by the sum of point distances for a design with 0.25 contactsfor each electrode per side.

FIG. 10 shows dimensionless ratios of charge travel distance as afunction of the number of contacts per edge for an active area. The plot1000 shows the dimensionless ratio of charge travel distance along they-axis 1010 and corresponds to the second column 902 in FIG. 9. The plot1000 shows the number of contacts per electrode per module edge alongthe x-axis 1020 and corresponds to the third column 903 in FIG. 9. Thereduced charge travel distance quickly flattens out as the number ofcontacts per electrode per module edge increases beyond 5 contacts perside.

FIG. 11A shows a plan view of a photovoltaic (PV) module with aninterdigitated contact arrangement according to an embodiment of thepresent invention. PV module 1100 includes a substrate 1110, a bottomelectrode 1120 (illustrated by electrode pads 1122), a photovoltaicmaterial layer 1130 and a top electrode 1140. PVC 1100 shows anembodiment with a particular arrangement of electrode pad/contact pointconnections 1112 for the efficient charge (power) extraction from thesubstrate 1110. In some embodiments, the placement of top electrode pads1132 with respect to the bottom electrode pads 1122 can vary. Forexample, PV module 1100 includes just one top electrode pad 1132 perside versus single cell module 800 in FIG. 8 which incorporated four topelectrode pads per side.

FIG. 11B shows an exploded view of PVC 1100 with an interdigitatedcontact arrangement. FIG. 11B includes a substrate 1110, a bottomelectrode 1120, a photovoltaic material layer 1130, a top electrode1140, and a particular arrangement of electrode pad/contact pointconnections 1112. It should be appreciated that the specific layersillustrated in FIG. 11B provide a particular arrangement of a PV withinterdigitated contacts according to an embodiment of the presentinvention. Other layers or contacts may also be formed thereon accordingto alternative embodiments. Moreover, the individual module layers andcomponents illustrated in FIG. 11B may include multiple sub-layers thatmay be formed and/or fabricated in various arrangements as appropriateto the individual module. Furthermore, additional layers or componentsmay be added or existing layers or components may be removed dependingon the particular applications. One of ordinary skill in the art wouldrecognize many variations, modifications, and alternatives.

FIGS. 12A-12B show photovoltaic cells according to various geometricarrangements according to an embodiment of the present invention.Embodiments that implement a continuous busbar and/or interdigitatedcontacts can facilitate design and fabrication of various sizes andaspect ratios. For example, FIG. 12A shows a square PVC 1210 with 8contact points 1212 per side. FIG. 12B shows a rectangular PVC 1212 with8 contact points 1222 per side. Scaling PVC 1210 in a first direction tofabricate PVC 1212 can be achieved with minimal scaling and interfacechanges as the number of contact points can remain the same and, alongside 1240, the module dimensions and contacts do not change. In someembodiments, the number of contacts on each side can be easily changeddepending on design requirements. These design requirements couldinclude increasing the number of contacts to reduce resistance (shorterpath-lengths); decreasing the number of contacts for simplicity ofmaking electrical contact to applications; decreasing the number ofcontacts to change contact widths if there are connection constraints;and removing the contacts from one edge. The number of contacts on eachside do not need to be equal.

In addition to the contact flexibility illustrated in FIGS. 12A and 12B,FIG. 13 shows the geometric flexibility of some embodiments. FIG. 13shows a photovoltaic cell according to a circular arrangement accordingto an embodiment of the present invention. The photovoltaic cellincludes a first transparent electrode layer 1310 that includes acontiguous first central region 1314. The first transparent electrodelayer also includes a first set of electrode pads 1312 electricallycoupled to the contiguous first central region 1314. The photovoltaiccell also includes a second transparent electrode layer 1320 thatincludes a contiguous second central region 1322 and a second set ofelectrode pads 1324 that are electrically coupled to the contiguoussecond central region 1322. The photovoltaic cell further includes aphotovoltaic material layer 1330 located between the first transparentelectrode layer 1310 and the second transparent electrode layer 1320.

The contiguous first central region 1314, the contiguous second centralregion 1322, and the photovoltaic material layer 1330 are aligned toform a central transparent area 1350 of the photovoltaic module. Thecentral transparent area 1350 has a perimeter that includes a pluralityof segments 1352. At least one of the first set of electrode pads 1312and at least one of the second set of electrode pads 1324 are positionedon each segment 1352 of the plurality of segments of the perimeter ofthe central transparent area 1350.

Non-rectangular geometries can be implemented using a single cell moduledesign because the added complexity of sub-cell sizes and connectionsare no longer a consideration. The single cell module design can beapplied to other standard shapes or even asymmetric abstract geometries.One of ordinary skill in the art would recognize many variations,modifications, and alternatives.

FIG. 14 shows a perspective view of various methods of contacting asingle cell module 1400. In some embodiments, the particular applicationwill influence the selection of a contact method. For example, contactto the single cell module 1400 can be made using solder connections 1410for applications that do not require frequent connect/disconnect cycles.In some embodiments, contact to the single cell module 1400 can also beimplemented using anisotropic electronic connectors 1420 (e.g., ZEBRA®connectors), which consist of alternating conductive and insulatingregions in a rubber or elastomer matrix. anisotropic electronicconnectors 1420, when compressed in a rigid fixture, can make electricalcontact to the interdigitated contacts of the single cell module 1400.In some embodiments, pin connections 1430 to contact points can be used.In some embodiments, alternating pin connections 1430 can beconnected/bundled together (on a PCB or some other combined circuit) toprovide a single anode and a single cathode connection for applying aload to the single cell module 1400. In some embodiments, contact to thesingle cell module can be made using flex-on-glass (FOG) anisotropicconductive adhesive 1440. An anisotropic conductive material can be usedas the anisotropic conductive adhesive 1440. In addition to theembodiments shown, other permanent or temporary contact methods can alsobe employed such as alligator clips, custom clamp fixture, and the like.Contact components can be very low resistance and power losses throughthese components can be negligible.

FIG. 15A is a cross-sectional view of a single cell module with aperimeter busbar for one or more electrodes according to an embodimentof the present invention. FIG. 15B is a perspective view of a singlecell module with perimeter busbar for one or more electrodes accordingto an embodiment of the present invention. FIG. 15A shows across-sectional view of FIG. 15B at line A.

The single cell module 1500 can include a bottom electrode layer 1510including a top surface, a bottom surface, and a plurality of sides. Insome embodiments, the bottom electrode layer 1510 can be comprised of amaterial that is transparent to visible light. In some embodiments, afirst set of contact pads 1554 can be fabricated in the same layer asthe bottom electrode layer 1510. Both the bottom electrode layer 1510and the first set of contact pads 1554 can include one or more lowresistance contact points 1556. The single cell module 1500 can alsoinclude one or more photovoltaic material layers 1520 including a topsurface, a bottom surface, and a plurality of sides. In someembodiments, the one or more photovoltaic material layers 1520 can betransparent to visible light. In some embodiments, the single cellmodule can include a top electrode layer 1530 including a top surface, abottom surface, and a plurality of sides. The top electrode layer 1530can be transparent to visible light.

In some embodiments, the single cell module can include a perimeterbusbar 1540 and a busbar extension 1550. The perimeter busbar 1540 canbe in contact with at least a portion of each side of the plurality ofsides of the top electrode to provide a low resistance pathway forcharge extracted in the top electrode 1530 to reach the busbar extension1550 on the edge of the single cell module 1500. Different busbarpatterns can be designed as needed to bus charge to different locationsfor contact. In some embodiments, as discussed in relation to FIG. 16, asimilar perimeter busbar can also be used to aid in moving charge fromthe bottom electrode. In some embodiments, perimeter busbar 1540 isopaque and can define, for instance, in conjunction with an aperture, anactive area 1560 as illustrated in FIG. 15A where light can impinge onthe single cell module 1500. The active area 1560 can include acontiguous central region of the top electrode 1530, a contiguouscentral region of the photovoltaic material layer 1520, and a contiguouscentral region of the bottom electrode 1510.

In the some embodiments, the perimeter busbar 1540 illustrated in FIGS.15A and 15B provides a pathway to transport current between electrodesand contact points 1556. The bottom electrode layer 1510 can include oneor more electrode pads 1552. Each electrode pad can have one or morecontact points 1556 to form an interface for the single cell module1500. In some embodiments, two or more sets of electrode pads can beinterdigitated. For example, a first set of electrode pads 1554 can beelectrically isolated from the bottom electrode layer 1510. Theperimeter busbar 1540 can be in electrical contact with the first set ofelectrode pads 1554. A second set of electrode pads 1552 can be inelectrical contact with the bottom electrode 1510.

FIG. 16A is a plan view of a single cell module with busbars in contactwith the perimeter of an electrode according to an embodiment of thepresent invention. The single cell module 1600 includes a substrate1610, a second busbar 1620, a bottom electrode 1630, one or morephotovoltaic material layers 1640, a top electrode 1650, and a firstbusbar 1660. In some embodiments the first busbar 1660 and the secondbusbar 1620 form a contact around the full module perimeter on the topelectrode 1650 and the bottom electrode 1610, respectively. In someembodiments with a 4-sided module, the full module perimeter can bedivided into four quadrants with the first busbar 1660 and the secondbusbar 1620 forming contacts in each of the four quadrants. In someembodiments, to maximize edge contact, the second busbar 1620 can fullycontact the bottom electrode 1610 around the full module perimeter (all4 sides) and the first busbar 1660 can fully contact the top electrode1650 around the full module perimeter (all 4 sides). To avoid electricalcontact between the first busbar 1660 and second busbars 1620, aninsulating layer covering the second busbar 1620 can be patternedanywhere the top electrode 1650 or first busbar 1660 overlaps the secondbusbar.

FIG. 16B is a first cross-sectional view of a single cell module withbusbars in contact with the perimeter of an electrode according to anembodiment of the present invention. FIG. 16C is a secondcross-sectional view of a single cell module with busbars in contactwith the perimeter of an electrode according to an embodiment of thepresent invention. FIG. 16B is a cross section that corresponds to line16B in FIG. 16A. FIG. 16C is a cross section that corresponds to line16C in FIG. 16A.

In some embodiments, the one or more photovoltaic material layers 1640and optional buffer materials can serve as an isolating buffer betweenthe top electrode 1650 and the bottom electrode 1610 where they overlap.The one or more photovoltaic material layers 1640 and optional buffermaterials can also be used to isolate the first busbar 1660 layer andsecond busbar 1620 layer. FIG. 16B shows the first busbar 1660 inelectrical contact with the top electrode 1650 and extending to a firstedge 1670 of the module. The first busbar 1660 is isolated from thebottom electrode and bottom busbar 1660 by the photovoltaic materiallayer 1640. FIG. 16C shows the second busbar 1620 in electrical contactwith the bottom electrode 1610 and extending to a second edge 1680 ofthe module. The second busbar 1620 is isolated from the top electrode1650 and the first busbar 1660 by the photovoltaic material layer 1640.In some embodiments, an additional insulating layer (not shown) can bedeposited over the bottom busbar 1620 to serve as an insulator toisolate the bottom busbar 1620 from electrical contact with the topelectrode 1650 or top busbar 1660.

As described above, one method for reducing the power loss caused by theresistance of the electrode layer is to use a busbar that can providecontact with an electrode layer around the full module perimeter. Tomaximize edge contact, a bottom busbar can be configured to contact thebottom electrode around the full module perimeter (i.e., all 4 sides)and a top busbar can be configured to fully contact the top electrodearound the full module perimeter (i.e., all 4 sides). In otherimplementations, in order to avoid electrical contact between the bottombusbar (and the bottom electrode) and the top busbar (and the topelectrode), a cutout area in the bottom busbar (and the bottomelectrode) and/or the top busbar (and the top electrode) can be used forconnecting the top busbar and/or the bottom busbar to contact pads ofthe single cell module.

FIGS. 17A-17F show a breakout of each layer of a single cell module withbusbars in contact with the perimeter of an electrode. FIG. 17A shows asingle cell module 1700 that can include a substrate layer 1710. In someembodiments, the substrate layer 1710 can include one or more electrodepads, including one or more bottom electrode pads and/or one or moreisolated electrode pads that are electrically isolated from the bottomelectrode pads. FIG. 17B shows a first busbar layer 1720 that can becoupled to the substrate layer 1710. In some embodiments, the firstbusbar layer can have an opening or void formed therein.

FIG. 17C shows a first electrode layer 1730 that can be fabricated inthe opening or void of the first busbar layer. In some embodiments, thefirst electrode layer 1730 can be an opaque electrode layer, atransparent electrode layer, or some combination thereof. In otherembodiments, an insulating material can be formed around the perimeterof the first electrode layer 1730. FIG. 17D show one or morephotovoltaic material layers 1740 that can be coupled to one or more ofthe substrate layer 1710, the first busbar layer 1720, and firstelectrode layer. In some embodiments, the one or more photovoltaicmaterial layers 1740 can be conventional photovoltaic materials, organicphotovoltaic materials, or some combination thereof. In someembodiments, the one or more photovoltaic material layers 1740 can betransparent.

FIG. 17E shows a second electrode layer 1750 that can be coupled to theone or more photovoltaic material layers 1740. The second electrodelayer 1750 can be an opaque electrode layer, a transparent electrodelayer, or some combination thereof. FIG. 17F shows a second busbar layer1760 that can be coupled to the second electrode layer 1750. In someembodiments, The optional insulator and the one or more photovoltaicmaterial layers 1740 can electrically isolate the second busbar layer1760 and second electrode layer 1750 from the first busbar layer 1720and the first electrode layer 1730. It should be appreciated that thespecific layers described in FIGS. 17A-17F provide a particularembodiment for forming a transparent photovoltaic single cell module.One of ordinary skill in the art would recognize many variations,modifications, and alternatives.

FIG. 17G shows an exploded view of a single cell module with the busbarsin contact with the perimeter of an electrode. The single cell module1700 includes a substrate layer 1710, a first busbar layer 1720, a firstelectrode layer 1730, one or more photovoltaic material layers 1740, asecond electrode layer 1750, and a second busbar layer 1760. It shouldbe appreciated that the specific layers illustrated in FIG. 17G providea particular arrangement of a single cell module with busbars in contactwith the perimeter of an electrode according to an embodiment of thepresent invention. Other layers or contacts can also be formed thereonaccording to alternative embodiments. Moreover, the individual modulelayers and components illustrated in FIG. 17G can include multiplesub-layers that can be formed and/or fabricated in various arrangementsas appropriate to the individual module. Furthermore, additional layersor components can be added or existing layers or components can beremoved depending on the particular applications. One of ordinary skillin the art would recognize many variations, modifications, andalternatives.

FIGS. 18A-18J show a breakout of each layer of an example single cellmodule with busbars providing near full perimeter contact with anelectrode layer according to an embodiment of the present invention. Thesingle cell module 1800 can include a bottom electrode layer 1810, abottom busbar layer 1820, an active layer 1830, a top electrode layer1840, and a top busbar layer 1850. As discussed above, or purposes ofclarity, references herein utilize the bottom/top nomenclature inreference to various figures, but it will be appreciated thatalternative fabrication processes and cell designs can be utilized inwhich first/second or right/left nomenclature could be appropriate.

FIG. 18A shows a bottom electrode layer 1810 that can include atransparent, electrical conductive material layer, such as an indium tinoxide (ITO), aluminum zinc oxide (AZO), antimony tin oxide (ATO),fluorine tin oxide (FTO), indium zinc oxide (IZO) layer, or thin metallayers such as aluminum, silver, gold or the like (4 nm-12 nm) coupledwith organic (e.g., small molecules) or inorganic dielectric layers(e.g. metal oxides). Bottom electrode layer 1810 can include a bottomelectrode 1812, where bottom electrode 1812 can include a contiguouscentral area and a number of extended areas 1814 extending beyond ancentral transparent area of single cell module 1800. In someembodiments, extended areas 1814 can extend to a first set of electricalcontact points 1860 of single cell module 1800. FIG. 18B shows amanufactured bottom electrode layer by a partial single cell module1815.

FIG. 18C shows a bottom busbar 1820 that can be formed on bottomelectrode layer 1810 or at least partially within bottom electrode layer1810. Bottom busbar 1820 can be implemented as a C-shaped bottom busbar1822, which can include a cutout area 1824 and one or more extendedareas 1826. Extended area(s) 1826 can be used to connect bottom busbar1822 and bottom electrode 1812 to electrode pads (not shown) of singlecell module 1800. Cutout area 1824 can be used for connecting topelectrode layer 1840 to contact pads at the bottom of single cell module1800 such that electrical contact between bottom busbar 1822 (and bottomelectrode 1812) and the top busbar (and the top electrode) can beavoided. FIG. 18D shows a second partial single cell module 1825including the bottom busbar 1820 formed on or at least partially withinbottom electrode layer 1810.

FIG. 18E shows an active layer 1830 that can be formed on bottomelectrode layer 1810 and/or bottom busbar layer 1820, and can includeone or more photovoltaic material layers as described above, such as acadmium telluride (CdTe) material layer, a silicon material layer, or alayer of another material that exhibits photoelectric effects. Activelayer 1830 can include an area 1832 that can at least partially coverthe C-shaped portion of bottom busbar 1822 to act as an isolation layerbetween the top electrode (and the top busbar) and bottom electrode 1812(and bottom busbar 1822). FIG. 18F shows a third partial single cellmodule 1835 including the active layer 1830 formed on bottom electrodelayer 1810, and bottom busbar 1820 formed on or at least partiallywithin bottom electrode layer 1810.

FIG. 18G shows a top electrode layer 1840 that can be formed on a sideof active layer 1830 opposite to bottom electrode layer 1810. Topelectrode layer 1840 can include a top electrode 1842 that can include acontiguous central area located at the active region of single cellmodule 1800. In some implementations, top electrode 1842 can include oneor more extended areas 1844 extending beyond the active region of singlecell module 1800. Extended areas 1844 can be used for connecting topelectrode 1842 to contact pads at the bottom of single cell module 1800.FIG. 18H shows a fourth partial single cell module 1845 including thetop electrode layer 1840 formed on top of active layer 1830, which canbe formed on bottom electrode layer 1810.

FIG. 18I shows a top busbar layer 1850 that can be formed on or at leastpartially within top electrode layer 1840. Top busbar layer 1850 caninclude a top busbar 1852. In some implementations, top busbar 1852 caninclude a C-shaped area and can include a cutout area 1854. Cutout area1854 can align with extended area 1826 on bottom bus bar 1822. In someimplementations, top busbar 1852 can include an annular-shaped area withno cutout region. Top busbar 1852 can include one or more extended areas1856. Extended area(s) 1856 can align with cutout area 1824 on bottombus bar 1822. Extended area(s) 1856 can be used to connect top busbar1852 to contact pads at the bottom of single cell module 1800. FIG. 18Jshows a manufactured single cell module 1845 including aligned layers ofbottom electrode layer 1810, bottom busbar layer 1820, active layer1830, top electrode layer 1840, and top busbar layer 1850.

FIG. 18K is an exploded view of the example single cell module 1800 withbusbars providing near full perimeter contact with an electrode layer.As described above, single cell module 1800 can include aligned layersof bottom electrode layer 1810, bottom busbar layer 1820, active layer1830, top electrode layer 1840, and top busbar layer 1850. Bottomelectrode layer 1810 can be formed on a substrate. In the example shownin FIG. 18B, bottom busbar 1822 can be formed on top of bottom electrodelayer 1810. In some implementations, bottom busbar 1822 can be formed onthe bottom surface of bottom electrode layer 1810 or formed at leastpartially within bottom electrode layer 1810. Active layer 1830 can beformed on top of bottom electrode 1812 or bottom busbar 1822. Topelectrode 1842 can be formed on active layer 1830, which can isolate topelectrode 1842 and bottom electrode 1812. Top busbar 1852 can be formedon top of top electrode 1842.

In some embodiments, in addition to or as an alternative to reducing theresistance of the electrode layer, a multi-junction cell module can beused to improve the efficiency of the single cell module by increasingthe output voltage of the single cell module while limiting the outputcurrent of the single cell module. As discussed above, operating at lowcurrent can help further reduce resistive power losses.

FIG. 19 is a cross-sectional view illustrating an example multi-junctioncell module according to an embodiment of the present invention.Multi-junction cell module 1900 can include multiple junctions (oractive layers) connected in series by interconnects between adjacentjunctions (or active layers) to form a tandem structure. As shown inFIG. 19, multi-junction cell module 1900 can include active layer 1(1980), active layer 2 (1960), active layer 3 (1940), . . . , and activelayer N (1920). The active layers can be connected in series bycorresponding interconnect layers 1970, 1950, 1930, etc. A top electrodelayer 1910 can be formed on active layer N (1920), and a bottomelectrode layer 1990 can be in contact with active layer 1 (1980). Eachactive layer and adjacent interconnect layers (or top electrode layer1910 and bottom electrode layer 1990) can form a subcell.

In multi-junction cell module 1900, the current generated in eachsubcell can flow in series to the electrodes. For example, in someimplementations, holes generated in active layer 1 (1980) can recombinewith electrons generated in active layer 2 (1960) at interconnect layer1970. Holes generated in active layer 2 (1960) can recombine withelectrons generated in active layer 3 (1940), and so on. As such, onlyholes from active layer N (1920) and electrons from active layer 1(1980) can be collected at the respective electrodes to generatephotocurrent. In some other implementations, the active layers and theelectrodes can be configured such that only holes from active layer 1(1980) and electrons from the active layer N (1920) can be collected atthe respective electrodes to generate photocurrent. The net outputcurrent in multi-junction cell module 1900 can be limited by the subcellthat generates the smallest current among all subcells. The outputvoltage of multi-junction cell module 1900 can be equal to the sum ofthe open-circuit voltages of the subcells because the subcells areconnected in series. For a multi-junction cell having N subcells madewith same active layers, the net short-circuit current generated by themulti-junction cell is approximately (J_(SC,single cell)/N), and the netopen-circuit voltage generated by the multi-junction cell isapproximately (V_(OC,single cell)×N), where J_(SC,single cell) is thenet short-circuit current of a single-junction cell andV_(OC,single cell) is the open-circuit voltage of a single-junctioncell. Because the net current is reduced by a factor of N, the powerloss due to the resistance of the electrode (even if unchanged) can bereduced by a factor of N as well. Thus, the overall efficiency of themulti-junction cell can be improved compared with a single-junctioncell.

A multi-junction cell is also more effective for area scaling than asingle-junction cell because the multi-junction cell can have a lowercurrent density at maximum power point (J_(MP)) and a larger voltage atthe maximum power point (V_(MP)) compared with the single-junction cell.Because power loss is directly proportional to J_(MP) and inverselyproportional to V_(MP), decreasing J_(MP) and increasing V_(MP) candecrease the power loss in multi-junction cells.

FIGS. 20A-20E illustrate current-density versus voltage plots forexample multi-junction cell modules with different numbers of junctionsand cell areas. FIG. 20A is a plot 2010 showing the relationship betweenthe voltage and the current density for a two-junction cell with anactive area of about 0.05 cm^(Z) and a two-junction cell with an activearea of about 2.5 cm². FIG. 20B is a plot 2020 showing the relationshipbetween the voltage and the current density for a four-junction cellwith an active area of about 0.05 cm² and a four-junction cell with anactive area of about 2.5 cm². FIG. 20C is a plot 2030 showing therelationship between the voltage and the current density for asix-junction cell with an active area of about 0.05 cm² and asix-junction cell with an active area of about 2.5 cm². FIG. 20D is aplot 2040 showing the relationship between the voltage and the currentdensity for an eight-junction cell with an active area of about 0.05 cm²and an eight-junction cell with an active area of about 2.5 cm². FIG.20E is a plot 2050 showing the relationship between the voltage and thecurrent density for a ten-junction cell with an active area of about0.05 cm² and a ten-junction cell with an active area of about 2.5 cm².

FIG. 20F is a table 2060 showing performance parameters of the examplemulti-junction cell modules with different numbers of junctions and cellareas described above with respect to FIGS. 20A-20E. As described above,power loss is generally directly proportional to the current producedand inversely proportional to the voltage produced. As shown by FIGS.20A-20F, increasing the number of junctions can decrease the totalcurrent extracted from the cell and increase the voltage as shown inFIG. 20F. Thus, the power loss of the multi-junction cell can decreasewith the increase in the number of junctions, and, with more junctions,the average efficiency of a multi-junction cell with a larger activearea can be closer to the average efficiency of a multi-junction cellwith a smaller active area. FIG. 20F shows that an area scaling factorabove 95% can be achieved across all junctions, and can increase withincreasing number of junctions.

In addition to reducing power loss, a multi-junction cell can provideother benefits. Many battery charging applications use input voltages of3.3 V, 5 V, or even higher voltages. Multi-junction cells can allow theoutput voltage of the single cell module to reach these higher voltages.For example, a single-junction cell can have an output voltage less than1 V (e.g., about 0.8 V). By combining multiple junctions in series, theoverall voltage can be much higher, such as 10 V or higher.

The output voltage from a module can be modulated using buck or boostconverters (or other types of regulators) that either down-regulate orboost up the voltage to match the input voltage of an applicationcircuit. With any regulation (either voltage up or down), there may be apower loss and thus an efficiency decrease. Stepping down in voltage isgenerally more efficient than stepping up in voltage, as thestepping-down regulators may not use as many components as thestepping-up regulators. Therefore, it may be desirable to tune themodule to match the output voltage of the module with the input voltageof the given application. In some implementations, the number ofjunctions can be altered to change the output voltage for differentapplications. In some implementations, the layer stack structure ratherthan the number of cells can be adjusted to vary the output voltage ofthe module such that no patterning or any other module geometry changesmay be needed in order to generate the different output voltage levels.

FIG. 21 is an exploded view illustrating a fixture assembly configuredto interface with a single cell module as described herein. In someembodiments, a fixture assembly 2100 can include a top fixture 2110, anencapsulated single cell module 2120, one or more connectors 2130, abottom fixture 2140, and/or a printed circuit board (PCB) 2150 tointegrate the single cell module with other modules and or devices. Insome embodiments, the one or more connectors 2130 can include one ormore wires or other conductive materials can be soldered or clamped tothe encapsulated single cell module 2120 at each contact point. In someembodiments the one or more connectors 2130 can include ZEBRA®connectors that press and make contact with the electrode contacts onthe glass and on the other side are connected to the printed circuitboard (PCB) 2150 that combines all the contacts from each electrode tofeed out 2 contact points (1 for the anode and 1 for the cathode). The 2output contacts can then be connected however desired for testing or toa load to power. In some embodiments, the one or more connectors canalso be implemented using elastomeric electronic connectors (registeredtrademark ZEBRA connectors), which consist of alternating conductive andinsulating regions in a rubber or elastomer matrix. These connectors,when compressed in a rigid fixture, can make a good electrical contactto the interdigitated contacts of the encapsulated single cell module2120 and conduct the charge through to contact pads on the PCB 2150. Afixture assembly can lower resistance caused by interfacing with thesingle cell module 2120 and minimize power losses from the moduleoutput.

It should be appreciated that the specific steps and devices describedherein provide a particular method of making a visibly transparentphotovoltaic module according to an embodiments of the presentinvention. Other sequences of steps may also be performed according toalternative embodiments. For example, alternative embodiments of thepresent invention may perform the steps outlined above in a differentorder. Moreover, the individual steps and devices described herein mayinclude multiple sub-steps that may be performed in various sequences asappropriate to the individual embodiments. Furthermore, additional stepsand components be added or removed depending on the particularapplications. One of ordinary skill in the art would recognize manyvariations, modifications, and alternatives.

It is also understood that the examples and embodiments described hereinare for illustrative purposes only and that various modifications orchanges in light thereof will be suggested to persons skilled in the artand are to be included within the spirit and purview of this applicationand scope of the appended claims.

What is claimed is:
 1. A photovoltaic module comprising: a firsttransparent electrode layer characterized by a first sheet resistance; asecond transparent electrode layer; a photovoltaic material layer, thephotovoltaic material layer located between the first transparentelectrode layer and the second transparent electrode layer; and a firstbusbar having a second sheet resistance lower than the first sheetresistance, wherein the first transparent electrode layer, the secondtransparent electrode layer, and the photovoltaic material layer have analigned region that forms a central transparent area of the photovoltaicmodule, the central transparent area including a plurality of sides; andwherein the first busbar is in contact with the first transparentelectrode layer adjacent to at least a portion of each of the pluralityof sides of the central transparent area.
 2. The photovoltaic module ofclaim 1, wherein the first busbar includes a C-shaped conductivematerial region surrounding the central transparent area of thephotovoltaic module.
 3. The photovoltaic module of claim 1, wherein thefirst busbar forms a closed loop surrounding the central transparentarea of the photovoltaic module.
 4. The photovoltaic module of claim 1,wherein the photovoltaic material layer comprises five or more junctionsconnected in series.
 5. The photovoltaic module of claim 1, wherein thephotovoltaic material layer comprises a plurality of junctions connectedin series.
 6. The photovoltaic module of claim 1, wherein the firsttransparent electrode layer or the second transparent electrode layercomprise an indium tin oxide (ITO) layer, a fluorine tin oxide (FTO)layer, an aluminum zinc oxide (AZO) layer, an antimony tin oxide (ATO)layer, an indium zinc oxide (IZO) layer, or a thin metal layer.
 7. Thephotovoltaic module of claim 1, wherein: the second transparentelectrode layer is characterized by a third sheet resistance; and thephotovoltaic module further comprises: a second busbar in electricalcontact with the second transparent electrode layer adjacent to at leasta portion of each of the plurality of sides of the central transparentarea, the second busbar having a fourth sheet resistance lower than thethird sheet resistance of the second transparent electrode layer.
 8. Thephotovoltaic module of claim 7, wherein: the second busbar includes aC-shaped or a closed loop conductive material region surrounding thecentral transparent area of the photovoltaic module.
 9. The photovoltaicmodule of claim 1, wherein each of the first transparent electrodelayer, the second transparent electrode layer, and the photovoltaicmaterial layer is contiguous in the central transparent area.
 10. Thephotovoltaic module of claim 1, wherein the photovoltaic material layercomprises a plurality of junctions connected in series.
 11. Thephotovoltaic module of claim 1, wherein the photovoltaic module isintegrated with an information display.
 12. The photovoltaic module ofclaim 1, wherein the first transparent electrode layer and the secondtransparent electrode layer each comprise an indium tin oxide (ITO)layer, a fluorine tin oxide (FTO) layer, an aluminum zinc oxide (AZO)layer, an antimony tin oxide (ATO) layer, an indium zinc oxide (IZO)layer, or a thin metal layer.
 13. A photovoltaic module comprising: afirst transparent electrode layer including: a contiguous first centralregion; and a first set of electrode pads electrically coupled to thecontiguous first central region; a second transparent electrode layerincluding: a contiguous second central region; and a second set ofelectrode pads electrically coupled to the contiguous second centralregion; and a photovoltaic material layer located between the firsttransparent electrode layer and the second transparent electrode layer,wherein the contiguous first central region, the contiguous secondcentral region, and the photovoltaic material layer are aligned to forma central transparent area of the photovoltaic module, the centraltransparent area including a plurality of sides; and wherein at leastone of the first set of electrode pads and at least one of the secondset of electrode pads are positioned on each of the plurality of sidesof the central transparent area.
 14. The photovoltaic module of claim13, wherein the first set of electrode pads is positionedinterdigitatedly with respect to the second set of electrode pads in atop plan view.
 15. The photovoltaic module of claim 13, wherein thephotovoltaic material layer comprises a plurality of junctions connectedin series.
 16. The photovoltaic module of claim 13, wherein thephotovoltaic material layer comprises five or more junctions connectedin series.
 17. The photovoltaic module of claim 13, wherein the firsttransparent electrode layer and the second transparent electrode layereach comprise an indium tin oxide (ITO) layer, a fluorine tin oxide(FTO) layer, an aluminum zinc oxide (AZO) layer, an antimony tin oxide(ATO) layer, an indium zinc oxide (IZO) layer, or a thin metal layer.18. The photovoltaic module of claim 13, further comprising: a busbar incontact with the first transparent electrode layer adjacent to each ofthe plurality of sides of the central transparent area, the busbarhaving a first sheet resistance, wherein the first transparent electrodelayer has a second sheet resistance greater than the first sheetresistance of the busbar.
 19. The photovoltaic module of claim 13,further comprising: a busbar in contact with the second transparentelectrode layer adjacent to each of the plurality of sides of thecentral transparent area, the busbar having a third sheet resistance,wherein the second transparent electrode layer has a fourth sheetresistance greater than the third sheet resistance of the busbar. 20.The photovoltaic module of claim 13, further comprising a connectorelectrically coupled to a plurality of the first set of electrode padsand a plurality of the second set of electrode pads, wherein theconnector includes at least one of an elastomeric electronic connector,an anisotropic conductive material, or a PCB.
 21. A photovoltaic modulecomprising: a first transparent electrode layer including: a contiguousfirst central region; and a first set of electrode pads electricallycoupled to the contiguous first central region; a second transparentelectrode layer including: a contiguous second central region; and asecond set of electrode pads electrically coupled to the contiguoussecond central region; and a photovoltaic material layer located betweenthe first transparent electrode layer and the second transparentelectrode layer, wherein the contiguous first central region, thecontiguous second central region, and the photovoltaic material layerare aligned to form a central transparent area of the photovoltaicmodule, the central transparent area having a perimeter that includes aplurality of segments; and wherein at least one of the first set ofelectrode pads and at least one of the second set of electrode pads arepositioned on each segment of the plurality of segments of the perimeterof the central transparent area.
 22. The photovoltaic module of claim21, wherein: the central transparent area of the photovoltaic module hasa circular shape; and the central transparent area of the photovoltaicmodule includes a plurality of sectors, each sector corresponding to asegment of the plurality of segments of the perimeter of the centraltransparent area.